Insensitive explosive materials that are more energetic and denser than those currently employed are necessary to satisfy current and future military requirements. The nitrated benzofuroxans are a family of explosives that have these properties. Nitrated benzofuroxans and the salts of some of their derivatives have been investigated as potential military explosives.
Most nitrated benzofuroxans are quite dense (approaching 2.0 g/cc) since they consist of quaternary carbons, tertiary nitrogens, and a few or no hydrogens. Since the nitrated benzofuroxans contain both nitro groups and furoxan rings, they are energetic (D'=7.9 to 9.0 mm/.mu.s). In addition, most nitrated benzofuroxans have been found to be rather insensitive to impact, friction, and electrostatic shock relative to other explosives of similar energy. Benzotrifuroxan (BTF) is an important explosive. Other important explosives are 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and 1,3,5-trinitro-1,3,5-hexahydrotriazine (RDX). Another benzofuroxan, aminonitrobenzodifuroxan (CL-18) has a higher melting point than its trinitro analogues but not as high as the dinitro compound, 7-amino-4,6-dinitrobenzofuroxan (ADNBF). The measured density and detonation velocity compares favorably to that of the other benzofuroxans and its impact sensitivity is favorable.
Aminonitrobenzodifuroxan (4-amino-5-nitrobenzo [1,2-c:3, 4-c'] bis [1,2,5] oxadiazole-3,8-dioxide) has been previously prepared in 24% overall yield from 1,3,5 trifluorobenzene as shown in FIG. 1: 1,3,5-trifluorobenzene was added to a solution of potassium nitrate and fuming sulfuric acid. The mixture was heated to produce 1,3,5-trifluoro-2,4,6-trinitrobenzene (3) (Reference 1). The trifluoro compound 3 was treated with acetamide in refluxing benzene to give 1 acetamido-3,5-difluoro-2,4,6-trinitrobenzene (4) (Reference 2). A solution of 4 in concentrated sulfuric acid poured onto crushed ice produced 1-amino-3,5-difluorotrinitrobenzene (5). The amine 5 was treated with sodium azide in acetonitrile-water to give the diazide 6, which when dissolved in toluene and heated at reflux produces aminonitrobenzodifuroxan (1, CL-18).
CL-18 was also prepared by employing the formamide and urea derivatives (5 and 6 where NH.sub.2 =NHCHO and NHCONH.sub.2, respectively) to form derivatives of 1 with these substituents. These derivatives were also subsequently hydrolyzed to 1.
The trifluorobenzene is an expensive starting material and the synthesis based on this starting material requires 5 steps and the isolation of four different intermediates.
This synthesis is economically inefficient and does not reliably produce high purity CL-18. This method often results in the production of mixtures of CL-18 with other benzofuroxan derivatives or in the production of low-purity CL-18. It is not recommended for scale up to a pilot plant or commercial plant for production of large quantities of CL-18.